A number of hydrocarbons, especially lower boiling-point light hydrocarbons, in porous media or natural gas fluids, are known to form hydrates in conjunction with the water present under a variety of conditions—particularly at a combination of lower temperature and higher pressure. The hydrates are solid crystalline compounds which co-exist with the surrounding porous media or natural gas fluids. Any solids in produced fluids are at least a nuisance for production, handling, and transport of these fluids. It is not uncommon for solid hydrates to cause plugging and/or blockage of pipelines or transfer lines or other conduits, valves and/or safety devices and/or other equipment, resulting in shutdown, loss of production, and risk of explosion or unintended release of hydrocarbons into the environment either on-land or off-shore. Accordingly, hydrocarbon hydrates have been of substantial interest as well as concern to many industries, particularly the petroleum and natural gas industries.
Natural gas hydrates are in a class of compounds known as clathrates, and are also referred to as inclusion compounds. Clathrates consist of cage structures formed between a host molecule and a guest molecule. Gas hydrates are generally composed of crystals formed by water host molecules surrounding the hydrocarbon guest molecules. The smaller or lower-boiling hydrocarbon molecules, particularly C1 (methane) to C4 hydrocarbons and their mixtures, are often the most problematic in the oil and gas industry because they form in hydrate or clathrate crystals under a wide range of production conditions. Even certain non-hydrocarbons such as carbon dioxide and hydrogen sulfide are known to form hydrates under the proper conditions. Beyond being a problem for production of hydrocarbons, hydrates are being looked at as a possible energy source.
At this time the only know method for determining the composition of a hydrate found in a subterranean reservoir is to monitor the composition of gases released by the dissociation of the hydrate. This is accomplished either by sampling a hydrate-bearing core that was brought to the surface, or by collected gases in the subterranean reservoir. Preservation of hydrate-bearing cores as they are brought to the surface in coring devices is problematic as the surrounding temperatures and pressures fall outside the thermodynamic stability zones. While some hydrate remains in the core there is concern that it does not represent the composition of the original. The collection of gas samples in a borehole with the intent of bringing the sample to the surface for analysis is also difficult, especially in obtaining an uncontaminated sample. Therefore, a need exists for identifying one or more characteristics, including the composition of the actual hydrate, within the subterranean reservoir.